1. Field of the Invention
The present invention relates generally to the architecture of semiconductor devices, and more particularly, to the architecture of a semiconductor device capable of mirror-symmetrically inverting input/output pin signal allocation when viewed from the outside.
2. Description of the Background Art
In the manufacture of conventional semiconductor devices, products having pins bent in one direction and in the opposite direction (hereinafter referred to as forward bent products and reverse bent products) are separately manufactured in order to eliminate the necessity of providing a stub line for matching impedance between chips when they are packaged onto a board.
FIG. 9 is a view showing the concept of how a forward bent product 100 and a reverse bent product 101 are packaged opposite to each other on the front and rear surfaces of a board 10.
Thus, the lengths of lines to these two chips may be not only made equal but also reduced, which contributes to reduction of ringing or the packaging area.
FIGS. 10A and 10B show a pin arrangement of the packages of such forward bent product 100 and reverse bent product 101.
Dark input/output pins as arranged in the right half of the package of forward bent product 100 are arranged in the left half in reverse bent product 101, in other words arranged mirror-symmetrically with respect to the central line.
Thus separately manufacturing the forward bent products and reverse bent products as described above is encountered with the following problem in view points of assembly cost and testing cost for chips.
More specifically, if a package is a so-called QFP (Quad Flat Package), in the process of bending the pins of a package, the pins are simply bent in different directions between forward bent products and reverse bent products.
The separate manufacturing of forward bent products and reverse bent products does not greatly affect the assembly cost.
However, the forward bent product and reverse bent product having different interconnection specifications require different testing boards depending upon the direction of bending in the process of testing. More specifically, an increased number of testing boards should be produced, which pushes up the testing cost.
If the package used is a so-called BGA (Ball Grid Array) package, strictly speaking, there is no such process of bending the pins of a package, but the term "forward bent product" and "reverse bent product" are still used as is the case with the QFP for ease of description.
FIG. 11 shows the concept of how a BGA package is installed.
The BGA package includes a semiconductor element 801, a package board 802, and solder ball terminals 804. Semiconductor element 801 is formed on package board 802. Solder ball terminals 804 are provided under package board 802. Semiconductor element 801 and solder balls 804 are electrically connected with each other.
During packaging, a tape carrier 810 having a tape of an organic material such as polyimide and a copper (Cu) interconnection thereon is welded with the solder balls.
The above-described structure of the BGA package permits the reverse bent product to be manufactured by changing the trace pattern on the polymide tape. The testing cost at the time itself therefore does not depend on the direction of bending.
Meanwhile, for the assembling cost, manufacturing a reverse bent product in the BGA package is equivalent to changing the trace pattern, and therefore the polyimide tape should be formed into a multilayer structure, which pushes up the assembling cost.